Summary of Significant Accounting Policies Restricted Cash (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Settlement agreement installment paid	$ 1,400	$ 10,300
Cash and cash equivalents in balance sheet	34,281	46,407
Restricted cash, current portion in balance sheet	399	4,597
Total cash, cash equivalents and restricted cash in statements of cash flows	34,680	$ 51,004	$ 39,690	$ 13,021
Letter of Credit
Decrease in restricted cash	$ 4,200